1. Field of the Invention
The present invention relates to a rotational angle sensor to be used for detecting a rotational angle of an object, and more particularly to a non-contact type rotational angle sensor for detecting a rotational angle of an object in non-contact therewith by converting the rotational angle to a change in magnetic force, and a sensor core used in the non-contact type rotational angle sensor.
2. Description of Related Art
Conventionally, there have been known contact type rotational angle sensors using a potentiometer. This potentiometer is constructed such that a wiper slides on a resistance element, thereby changing electrical resistance values. Accordingly, dust particles resulting from friction between the resistance element and the wiper may be generated in a sliding portion therebetween. The dust particles would cause detection errors in the resistance values. Furthermore, a frictional resistance in the sliding portion may become an operating resistance to an object to be detected, which affects the operating responsivity of the object.
As a rotational angle sensor to resolve the above disadvantages of the contact type rotational angle sensor, a non-contact type with no sliding member or portion has been developed. One of such the non-contact type rotational angle sensors is constructed to detect a rotational angle of an object in non-contact therewith by converting the rotational angle to a change in magnetic force. Japanese patent No. 2,842,482 and Japanese patent unexamined publication No. 8-35809 disclose an example of the non-contact type rotational angle sensor of this kind.
FIG. 25 shows main parts of the rotational angle sensor disclosed in Japanese patent No. 2,842,482. This rotational angle sensor is provided with a cylindrical case 51 and a connecting shaft 52 disposed rotatably in the center of the case 51. A first member 53 is fixed on the inner peripheral surface of the case 51. The first member 53 is constituted of two semicircular rings 53A and 53B, both made of a soft magnetic material. Between the semicircular rings 53A and 53B there are provided two sub-air-gaps 54. An electric coil 56 is arranged in one gap 54, and a Hall probe is arranged in the other gap 54. A second member 57 made of a soft magnetic material is fixed on the connecting shaft 52. A tubular magnet 58 constructed of two thin members 58A and 58B is fit on the outer periphery of the second member 57. The tubular magnet 58 is made of mold samarium-cobalt formed and magnetized in a tubular shape. A main-air-gap 59 is disposed between the tubular magnet 58 and the first member 53. The main-air-gap 59 is desired to be as narrow as possible. In the above publication, if the average inner diameter of the second member 57 is 5 mm and the thickness of the tubular magnet 58 is 1 mm, then the width of the main-air-gap 59 is of the order of 0.2 mm. Thus, a magnetic field is generated between the first member 53 and the tubular magnet 58 and the second member 57. When the second member 57 and the tubular magnet 58 are rotated together with the connecting shaft 52, the magnetic field is rotated, thereby changing the density of magnetic flux passing through the Hall probe 56 and the electric coil 55. The change in the magnetic flux density is output in the form of electric signals.
FIG. 26 shows main parts of the rotational angle sensor disclosed in Japanese patent unexamined publication No.8-35809. This rotational angle sensor is provided with a tubular yoke 61 and a driven shaft 62 disposed in the center of the yoke 61, both being integrally configured. A tubular permanent magnet 63 is fixedly provided on the inner peripheral surface of the tubular yoke 61 made of a soft magnetic material. The tubular magnet 63 has been magnetized in a radial direction in cross-section. Around the driven shaft 62, two separated tubular stators 64A and 64B are fixedly disposed. The driven shaft 62 is allowed to rotate in a central area surrounded by the stators 64A and 64B. A Hall element 66 is provided in a gap 65 between the two stators 64A and 64B. The tubular yoke 61 and the tubular magnet 63 are arranged rotatably with respect to the stators 64A and 64B. An annular air-gap 67 is produced between the tubular magnet 63 and the stators 64A and 64B. Thus, a magnetic field is generated between the tubular yoke 61, the tubular magnet 63, and the stators 64A and 64B. Accordingly, rotation of the tubular magnet 63 together with the tubular yoke 61 causes rotation of the magnetic field, thereby changing the density of magnetic flux passing through the Hall element 66. The change in the magnetic field density is output in the form of electrical signals.
In the rotational angle sensor of Japanese patent No. 2,842,482, however, the tubular magnet 58 is made of mold samarium-cobalt formed and magnetized in a tubular shape with a very small thickness of about 1 mm, which would be very physically brittle and hard to manufacture. In addition, the tubular magnet 58 after fit on the outer periphery of the second member 57 has to be assembled with the shaft 52 while keeping the extreme narrow main-air-gap 59 with respect to the first member 53. Therefore, in assembling, even a slight inclination of the tubular magnet 58 or the first member 53 may bring them into contact, which would easily damage the tubular magnet 58. This results in difficulty in manufacturing the rotational angle sensor and deterioration in the accuracy of detection of a rotational angle.
In the rotational angle sensor of Japanese patent unexamined publication No. 8-35809, on the other hand, there is a problem that it is difficult to manufacture the tubular magnet 63. In addition, the tubular magnet 63 has to be fixed on the inner peripheral surface of the tubular yoke 61 and, inside of the magnet 63, the stators 64A and 64B are needed assembling with the air-gap 67 of a predetermined dimension. During assembly, contact between the tubular magnet 63 and the stators 64A and 64B would cause damage to them. This makes it difficult to manufacture the rotational angle sensor and also causes deterioration in the accuracy of detection of a rotational angle.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a non-contact type rotational angle sensor capable of providing enhanced productivity of magnets, sensor cores with the magnets, and rotational angle sensors, and improved assembling property of parts and elements to enhance the accuracy of detection of a rotational angle, and a sensor core used in the sensor.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a sensor core used in a non-contact type rotational angle sensor for detecting a rotational angle of an object in non-contact therewith by converting the rotational angle to a change in magnetic force, the sensor core including: a stator core provided with two blocks made of a magnetic material; a mover core provided with two blocks made of a magnetic material, disposed coaxially with the stator core; a first gap produced between the stator core and the mover core; a second gap produced between the two stator blocks; a third gap produced between the two mover blocks; and a rectangular parallelepiped magnet disposed in the third gap and magnetized in a direction across the third gap to connect the mover blocks.
In the above sensor core, preferably, a shape of one of the stator core and the mover core is determined to produce the first gap with a dimension changing to become largest in a vicinity of a center line of the second gap.
Alternatively, both shapes of the stator core and the mover core are determined to produce the first gap with the dimension changing to become largest in the vicinity of the center line of the second gap.
Preferably, the shape of one of the stator core and the mover core is determined so that the dimension of the first gap changes stepwise.
In the above sensor core, preferably, the shape of one of the mover core and the stator core is determined to include a taper surface or an elliptic surface so that the dimension of the first gap changes continuously.
According to another aspect of the present invention, there is provided a non-contact type rotational angle sensor using the sensor core including a rotor constructed of the magnet mounted in the third gap of the mover blocks, the sensor including: a base for fixing the stator core; and magnetic force detecting means disposed in the second gap, for detecting a change in magnetic force in response to rotation of the rotor; the rotor being to be connected with the object.
In the above non-contact type rotational angle sensor, preferably, both shapes of the stator core and the mover core are determined to produce the first gap with the dimension changing to become largest in the vicinity of the center line of the second gap.
Preferably, the shape of one of the stator core and the mover core is determined so that the dimension of the first gap changes stepwise.
In the above non-contact type rotational angle sensor, preferably, the shape of one of the mover core and the stator core is determined to include a taper surface or an elliptic surface so that the dimension of the first gap changes continuously.